A typical lighting system can include a luminaire, that is, a series of one or more light emitting diode (LED) bulbs, having a power supply (e.g., a LED driver) and a controller, which can include a DALI network.
In general, a DALI network includes a controller and one or more lighting devices (e.g., electrical ballasts and dimmers) that have DALI interfaces. The controller can monitor and control each light by means of a bi-directional data exchange. The DALI protocol permits devices to be individually addressed and it also incorporates Group and Scene broadcast messages to simultaneously address multiple devices.
Each lighting device is assigned a unique static address in the numeric range 0 to 63, making possible up to 64 devices in a standalone system. Alternatively, DALI can be used as a subsystem via DALI gateways to address more than 64 devices. Data is transferred between controller and devices by means of an asynchronous, half-duplex, serial protocol over a two-wire bus, with a fixed data transfer rate of 1200 bit/s.
DALI requires a single pair of wires to form the bus for communication to all devices on a single DALI network. The network can be arranged in a bus or star topology, or a combination of these. The DALI System is not classified as separated extra low voltage (SELV) and therefore may be run next to the mains cables or within a multi-core cable that includes mains power. The DALI data is transmitted using manchester encoding and has a high signal to noise ratio, which enables reliable communications in the presence of a large amount of electrical noise.
DALI employs a diode bridge in the interface circuitry so that devices can be wired without regard for polarity. Signal level are defined as 0±4.5 V for “0” and 16±6.5 V for “1”. Central interface power maximum is 250 mA and 2 mA per unit. The network cable is required to be mains-rated, with 600 V isolation and at least a 1 mm cross-section, with a maximum drop of 2 volts along the cable (max 300 m). Signal interface is galvanically separated and doesn't need any termination resistors.
Earlier generations of DALI devices stored configuration data in EEPROM, which was problematic due to the limited number of write cycles supported by EEPROMs. In current generations of DALI devices, RAM is used in preference to EEPROM during normal operation, which significantly reduces the number of EEPROM writes and thus extends their lifetimes.
In the lighting system, the control system sends messages to a microcontroller in the DALI to for commands such as to power on and power off the luminaire. When the luminaire is powered off, the microcontroller in the DALI goes into a low power mode. It is important that the DALI is still able to receive messages and respond to commands from the controller when the microcontroller is in the low power mode. Often, when in the low power mode, the microcontroller is not able to respond to commands.